Renewable sources of energy - class-VIII

Answer is B.
Windmills, like waterwheels, were among the original prime movers that replaced animal muscle as a source of power. They were used for centuries in various parts of the world, converting the energy of the wind into mechanical energy for grinding grain, pumping water, and draining lowland areas.
Kinetic energy of the wind is transformed into mechanical energy of the turning windmill. This can be used to turn a generator to generate electricity. The original energy to cause the wind to blow came from the sun. Uneven heating of the earth's surface causes wind.
Hence, the statement is false.

Answer is B.

Biogas is characterized based on its chemical composition and the physical characteristics which result from it. It is primarily a mixture of methane (${ CH } _{ 4 }$) and inert carbonic gas (${ CO } _{ 2 }$). However the name 'biogas' gathers a large variety of gases resulting from specific treatment processes, starting from various organic waste - industries, animal or domestic origin waste, etc . 
Hence, the statement is false.

Fuel-grade ethanol is one energy source that has great potential for being generated from biomass. The gas obtained by the fermentation of biomass is called biogas.

Renewable energy is generally defined as energy that comes from resources which are naturally replenished on a human time scale such as sunlight, wind, rain, tides, waves and geothermal heat. Hence, Sun is naturally coming and can be used in the form of solar energy, to evaporate water which turns into rain and rains are useful in many uses. Ultimately, Sun is the renewable source of energy.

Renewable- (b), (c) and (e); Non-renewable- (a), (d) and (f).
Here once petrol,diesel, coal and oil are consumed, for example in our vehicle, it cannot come back and renew to some other thing where as in wood, wind and water once we use it for some purpose we can use it for some other thing again like if wood is used in making bed then again we can make it back to wood or some other thing. Hence, these are renewable sources.

Unlike fossil fuels, trees are eternal sources of energy for animals. They absorb sunlight directly from the environment and keep on producing food for others as long as they exist.

Renewable-(b), (c) and (e); Non-renewable-(a), (d) and (f).
Here once petrol, diesel, coal and oil are consumed, for example in our vehicle, it cannot come back and renew to some other thing whereas in wood, wind and water once we use it for some purpose we can use it for some other thing again like if wood is used in making bed then again we can make it back to wood or some other thing. Hence, these are renewable sources.

Answer is D.

The heat produced by either steam or coal is converted in to electrical energy. Thus, in a thermal power station, heat energy is converted to electrical energy.

Biogas is a type of secondary energy because biomass (primary energy) is used to produce biogas by anaerobic digestion into more efficient and higher value fuel.Biogas is also called gobargas as made by waste remains of plants and animals.

Major gases released from biomass are methane ($CH _4$), carbon dioxide ($CO _2$), hydrogen ($H _2$) and hydrogen sulphide ($H _2S$).

Tidal energy is caused by the gravitational pull of the Moon and Sun on Earth's oceans, which is distinct from direct solar radiation, though it is often categorized as a renewable energy source.

A solar cooker is a device which uses the energy of direct sunlight to heat or cook. A mirrored surface with high specular reflectivity is used to concentrate light from the sun on to a small cooking area. Depending on the geometry of the surface, sunlight can be concentrated by several orders of magnitude producing temperatures high enough to melt salt and smelt metal. 

There are two primary means of achieving desalination using solar energy, through a phase change by thermal input, or in a single phase through mechanical separation. Phase change (or multi-phase) can be accomplished by either direct or indirect solar distillation. Single phase is done by the use of photovoltaic cells to produce electricity to drive pumps.

The value of solar constant is fixed and it is equal to $1.951Kcal\quad m^{-2}minute^{-1}$  which can be rounded off.

Photons generated in the Sun's core undergo a random walk, colliding repeatedly with dense plasma particles, which significantly delays their journey to the surface.

Solar energy is the primary source for wind energy (via heating differences), light energy (direct radiation), and heat energy (thermal absorption).

The Sun generates energy primarily through nuclear fusion, where hydrogen nuclei fuse to form helium, releasing vast amounts of energy.

Wind power generation capacity in India has significantly increased in the last few years . The installed capacity of wind energy in India is about 8000MV.

Answer is C.

The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises, moving slowly up toward the earth's crust, carrying the heat from below.
Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth) - sometimes as hot as 700 degrees F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.
Hence, the super-heated steam is raised in geothermal plants by the heat of magma or lava.

The steam comes from reservoirs of hot water found a few miles or more below the earth's surface. The steam rotates a turbine that activates a generator, which produces electricity Hence Geothermal energy can be used to produce electricity.

Geothermal power plants are actually known for their ability to operate continuously (base load power), unlike solar or wind, making the claim that they cannot operate round the clock false.